Question on lawn pest (moles / grubs?)

Asked May 18, 2015, 9:16 PM EDT

I’ve attached several pictures from my yard of what I think may be grub/mole-induced damage, but I’m not sure. I purchased a grub-killing fertilizer (containing 0.25% Imidacloprid) which suggests to contact your local Extension Office for the optimal time of year for application in your region. I just mowed yesterday, so if I should apply, I could do so now. I would appreciate if you could check the images, and let me know if you think I do have a mole / grub issue, and if so, the optimal time of year for application in Ottawa County for such a treatment. I am not very educated in this area, and am open to any and all suggestions as to the root (no pun intended...) cause and corresponding countermeasures. I bought some mole killing fake worms, but am not sure if I’m deal with moles or not, or if this is best approach. Thank you in advance for your feedback and suggestions.

Ottawa County Michigan

3 Responses

The pictures are so tiny that they are smaller than stamps and do no enlarge to show much of anything.

Moles usually do not leave holes. Starnosed moles will leave a big pile of soil but the hole is not visible. Eastern moles leave tunnels just below the surface and have no reason to create an opening. A dog could dig into a tunnel or a person. The mole doesn't to get out, its home. If these were mole holes, they would lead to a tunnel. If the hole is just a couple of inches deep, it could be skunks or raccoons.

For moles, 80% of their diet is earthworms. The other 20% are soil insects and grubs. If you have moles, it does not follow that you have grubs. Applying a grub killer now will give you 0% control. It is a waste of time and money.

The digging in the back yard looks like skunks or raccoons. They dig for soil insects, earthworms and grubs and prefer to dig where the sod is thin. You are indicating it is under a tree and grass is thin because there is not enough sunlight for a dense turf.

If you had grubs worthy of treating it would be because you found areas of dead turf last late summer and fall. When you pulled on the grass, it came up easily with very short roots. Grubs would have eaten the roots.

Right now, imidacloprid is being tested to see if it is implicated in the death of bees. If you decide to apply it, do it the first week of July, not now. If there were grubs, they are too big to kill. You are waiting for these grubs, if there are any, (doubtful) to turn into beetles and lay eggs and you will be killing their small kids. Mow short to remove any flowers from weeds in the lawn if you are determined to kill grubs before applying this product. Follow the bag difrections.

You should be cutting your grass to a finished cut height of 3 1/2 inches. It looks like the grass almost appears "scalped" by the color in the tiny photo.

If there are moles, the starnosed leaves a pile of dirt and tunnels are 6-12 inches deep. If there are eastern moles, the tunnels are right below the surface and the turf is bumped up. Moles do not equal holes or grubs.

Hello Ms. Voyle,
Thank you for this helpful reply. I've raised my mower height based on your feedback. I also did the "pull on the grass" test you mentioned and in certain brown areas the grass did come up like poorly laid carpet. If applying imidacloprid would have no affect if applied now, but I am seeing fresh new brown areas which pull up like carpet, is there something I can do now before July (and more damaged sections appear)?

Based on your description the holes seem to be more the "skunk/raccoon" type. I have not seen these in our yard. Would squirrels (which I see often) also leave such small holes, too?

Regarding the image smallness of the original submission, in the original submission, I only found a way to upload one file, so I combined a few pictures into a single slide. I now see the option to include up to 3 images with this reply, so I'm including the original pictures which will be larger. I hope these are more helpful.

Thank you again for your helpful insights and tips!

Best Regards,
Caryl Brown

The photos are great. You figured it out, which is more than I could do!

Using a grub control product will not get rid of current grubs... they are too big. The photo with multiple holes looks like skunk damage or possibly raccoon. Grubs do very little damage in the spring because they will be emerging as adults in the next several weeks and are not feeding (they are pupating). Insect killers don't work on those that are not feeding. Adults do not feed on the lawn.

To limit problems with grubs, research has shown that raising your finished cut height to 3 1/2 inches and watering the lawn when dry and periodic fertilization (like three times a season) can help limit or prevent damage.

It appears that the sod closest to the driveway or sidewalk in the photo was laid on soil that was as high as the cement. When the sod was laid, it now was several inches higher that the cement. When you mow and one wheel is on the cement and the other on the turf, the cement side is getting a close shave.

Squirrels do not dig in the lawn because they do not eat anything there. They could be burying nuts but this is fall activity. Even if they were digging up bulbs, there would be not bulbs in the lawn.

You essentially have about a month until you can apply grub control. Be sure that no weeds are blooming at the time you apply and later so bees do not get dosed with the imidacloprid. Reasearch is suggesting that this product is harming bees.